Horizontal continuous casting apparatus



June 27, 1967 R. T. cRAxG ET AL 3,327,768

HORIZONTAL CONTINUOUS CASTING APPARATUS Filed Jan. 25, 1965 IGIO RichardCraig Y* BY Robe/'T E Dieffenbach ATTORNEY United States Patent O3,327,768 HGRIZNTAL CONTINUOUS CASTING APPARATUS Richard T. Craig, NewKensington, Pa., and Robert P.

Dieienhach, Davenport, Iowa, assignors to Aluminum Sompany of America,Pittsburgh, Pa., a corporation of Pennsylvania Filed Jian. 25, 1965,Ser. No. 427,716 4 Claims. (Cl. 164-2810 This invention relates tocontinuous casting in horizontally disposed molds, ingots of the lightmetals, aluminum and magnesium, together with alloys in which thesemetals constitute at least 75% by weight of the composition.

Horizontal continuous casting of ingots has found commercial acceptancebecause of generally recognized advantages in certain respects oververtical casting. For instance, vertically casting long ingots requireselevating the mold or providing a deep pit beneath it, either methodrepresenting a costly installation which is avoided in horizontalcasting. Other advantages are the degree of operating continuity and theingot handling convenience associated with horizontal casting.

In the horizontal casting under consideration here molten metal isprovided in a reservoir separated from the horizontal mold by a partialbarrier or closure which does not chill the metal, and hence can beconveniently made of an insulating or refractory material. This partialclosure, hereinafter referred to as the header plate, has a gate, oropening, for passage of the liquid metal therethrough and directly intoa drastically chilled mold wherein the metal is solidified andcontinuously withdrawn in a horizontal direction. The emerging ingot isthen conveniently cut to desired length without interrupting the castingoperation, the duration of a casting run depending only on the moltenmetal supply.

Horizontally cast light metal ingots often exhibit a surface defectcalled a lap or fold which corresponds to what is called la cold-shut invertically cast ingots. These lap defects, as explained in more detailhereinafter, appear as repeated band-like irregularities on the ingotsurface normal to the axis of the ingot and are generally attributed tovariations iri surface tension and metal freezing rates which occurduring initial contact of the metal with the drastically chilled mold.The laps or folds extend into or penetrate t-he surface of the ingotwhich generally necessitates removal of the affected surface portions toan extent commensurate with the depth of penetration before the ingot isfurther processed, especially if it is to be rolled. The lap penetrationproblem is generally most severe in horizontally cast ingots havingrelatively large cross-sections, e.g. one having rectangular dimensionsof l x 40, where the lap depth or penetration varies from less than 1Ain the top-most surface portion of the ingot to 3A or 1/2 or even morein the lower surface portions of the ingot. The difference in depth ofthe laps on the bottom and top surfaces of an ingot is considered to bedisproportionate. While there are some exceptions, this severe ordisproportionate lap penetration is most often observed in light metalalloys having a relatively wide freezing range. While the foregoingcondition in the top-most surface portion of the ingot is oftenconsidered commercially acceptable from the standpoint of the depth ofmetal to be removed, the deeper cut associated with the lower surfaceportions is generally deemed excessive.

It has been discovered that the severe lap penetration prevailing in thelower surface portions of a horizontally cast ingot can be alleviated byproper positioning of the gate opening with respect to the mold.

Accordingly a primary object of the invention is to 3,327,768 Patented.lune 27, 1967 ICC provide apparatus adapted to minimizedisproportionate lap penetration into the freezing ingot surface,especially at the lower surface portions thereof, in the continuoushorizontal casting of light metal ingots.

Another object of the invention to provide a method for continuouslycasting light metal ingots in horizontally disposed molds wherein lappenetration, particularly in the surface of the lower ingot portions, isminimized.

Further objects of the invention will, in part, be obvious and will, inpart, appear hereinafter.

For a better understanding of the invention and its objects reference ismade to the following description, including the appended claims and thedrawings in which:

FIGURE 1 is an elevation view, partly in cross-section, illustrating ahorizontal casting apparatus;

FGURE 2 is an enlarged longitudinal cross-section of a portion of ametal ingot freezing in a horizontal mold;

FIGURE 3 is an elevation in cross-section illustrating the invention inmore detail;

FIGURE 4 illustrates three ingots in cross-section indicating theperipheral zones of severe and disproportionate lap penetration.

Briefly, the invention resides in the discovery that the severe anddisproportionate lap condition prevailing in the lower surface portionsof horizontally continuous cast ingot can be minimized by introducingthe molten metal at a low flow rate in very close proximity to the innermold wall surface of an open ended mold shell using a gate opening onlyslightly smaller than the internal dimensions of the mold entrance. Thestream of molten metal moving into the mold should have a considerablyhorizontal attitude which, it has been found, exerts a disturbinginfluence on the laps penetrating into the ingot. Another factor is thatthe shape of the gate opening deilects the angular position of the lapspenetrating into the ingot toward an attitude parallel .to the moldaxis.

Referring now to the drawings, the general arrangement of a horizontalcasting apparatus embodying the invention is shown in FIGURE 1. Thereinis shown an open top molten metal reservoir 2 having walls of a suitablerefractory material 6, and having the general transverse shape of a Uand of sufficient width to embrace all of gate 20 in the header plate18. The header plate 18 consists of a vertical plate-like refractoryheat insulative material having an apperture 20 to permit the transferof metal 8 from the reservoir 2 through the header plate and into thechilled mold 10. The choice of refractory will be determined by thenature of the metal being cast, in the case of casting aluminum andaluminum base alloys the commercial asbestos-silica product sold underthe trade name Marinite is satisfactory. It is to be understood thatwhile the header plate is most conveniently fashioned from refractorymaterial, such is not an absolute necessity, It is only essential thatthe header plate does not significantly chill the liquid metal before itreaches the drastically chilled mold and hence the member is describedfunctionally in the claims as a nonchilling header plate. On theopposite side of the header plate 18 and compressed against it in asealing position is the chilled mold 10 which can be made of a suitableheat conductive material such as aluminum or copper or alloys in whichthese metals predominate. Although the mold can be made as an assembly,a more convenient arrangement is to make the mold as an integral castingand machine the surfaces where required, as well as any passageways. Themold is generally quite short even where large ingots are cast, typicalmold lengths ranging from about one to four inches. The mold has a lipor step at its entrance. This inwardly extending step may be provided bya separate metallic gasket 32 which has a slightly smaller opening thanthe mold 10 as shown. The use of such a gasket is described and claimedin co-pending application Ser. No. 286,349. Typical dimensions for thisinwardly extending short step are about l/ length (gasket 32 thickness)and 0.010" step extension into the mold opening. The mold may be cooledby circulation of water or other coolant supplied through pipe 14 tochamber 16 in the mold Wall. The coolant is discharged from chamber 16and projected as a sheath 52 onto the emerging ingot through channel S0.Alternatively, the mold without a surrounding cooling chamber may bechilled by suitably positioned water sprays. Also seen in FIG. l ispassageway 58 for continuously supplying lubricant to channel 34 fromwhere it is fed to the head of the mold at the inner wall surfacethrough suitable small openings which may be fashioned by cutting aseries of radially disposed notches 33 into the mold face to connect theoil channel 34 with the mold interior. Suitable means, not shown, areprovided for refractory back-up, structural support, etc.

The molten metal supply in relation to the solidified ingot is alsoevident in FIG. l where molten metal 8 in the reservoir passes throughthe gate 20 in the header plate 1S and establishes a molten head ofmetal 36 within the mold 10. lt should be noted that the molten metallevel in the reservoir is above the mold thereby furnishing a positiveliquid metal head. The metal coming in contact with theinner mold wallsurface freezes almost immediately to form the walls of the embryoingot, the freezing starting at 42 next to the header plate 18. The headof molten metal generally extends beyond the exit end of the mold, theboundary between liquid or semiliquid and solid metal being generallyillustrated for the ideal case by line 38. The molten metal progessivelyfreezes forming a solid ingot 40 which is moved away from the mold at acontinuous rate by means of power actuated rollers 54, or the like.While there has been described a particular species of horizontalcontinuous casting apparatus, it is not intended that the invention benecessarily limited thereto.

At this point a brief explanation is set forth as to what are believedto be the nature and the causes of lap development in ingot castingtogether with how such is affected by the practice of the invention. Itis observed in FIGURE l that laps appear on the ingot surface as aseries of bands, typified by the numeral 110, extending around theperiphery of the ingot in a plane substantially normal to the ingotaxis. In cross-section it is observed that the laps appear as a seriesof linear penetrations into the ingot and that a typical lap penetration130 across the top-most portion of the ingot is less than that 208 atthe bottom. For clarity purposes only a few laps are illustrated in FIG.l; however, it is to be understood that the lap defects prevail alongthe entire ingot length and that those shown are merely typical. Thepenetration at the top is typified by depth of generally not more thanabout 1A; to 1,/4 of an inch as opposed to the condition at the bottomportions where the penetration runs as deep as 3A" to 1/2" or more inlarge ingots. While the precise reason for this condition is notcompletely understood, the zones of maximum lap penetration appear to beassociated with the most drastically chilled regions which in turn areprobably determined by a combination of thermal and gravitation effects.The disproportionate lap penetration problem is generally mostpronounced with ingots of relatively large cross-section, for instance,by 40" rectangular cross-section. Also, while there are exceptions tothis general rule, alloys having relatively broad freezing ranges (80 F.to 200 F. and higher) are generally most susceptible to thedisproportionate lap penetration. FIGURE 2 is an enlarged cross-sectionof the lower portion of a freezing ingot emphasizing lap growth 208 intothe ingot. It can be seen that a band of discontinuities in grainstructure and composition, schematically typified by dotted linesparalleling the lap itself and the ingot surface and designated by thenumeral 209, ex-

tend a little further into the ingot than the actual lap itself and mustbe considered in removing surface material to prepare the ingot forfurther processing. The zone of severe lap penetration is describedherein as the lower surface portions but also generally extends aroundthe entire periphery excepting the top-most portion. For example FIGURE4o illustrates the periphery of an ingot of rectangular cross-sectionand the zones of minimal lap penetration, the top-most surface portion840, together with the zone of severe and disproportionate lappenetration, the lower surface portions 810. Similarly FIGURES 4b and crespectively illustrate this zone for circular and polygonalcross-sections. rfhus the term lower surface portions is intended'toencompass this zone which not only includes the bottom itself butextends up the sides and generally around the top corners.

It is believed that laps are caused by fluctuations in the surface skinof the ingot vas freezing is initiated. Referring to FIGURE 2 the liquidmetal at the junction of the non-chilling or refractory header plate 18and the mold 10, the liquid surface is shown as forming fa submergedfree liquid meniscus 220 which also forms 'the boundary of meniscus void210. The insert gasket 32 is not shown completely in FIG. 2 so that themeniscus effects may be more clearly illustrated. As the liquid metal ischilled, its surface becomes semi-solid, or plastic, a condition whereinit does not function as a liquid but cannot be considered a solid. Bythe effect of factors such as increased surface tension, freezingshrinkage and others, a freezing plastic meniscus 216 forms and extendsor grows into the embryo ingot substantially along the wall of headerIplate 18. This causes the meniscus gap 210 to significantly increasethus curtailing heat flow out of the freezing plastic meniscus zonewhich is thus weakened especially at the innermost portion 218. Theifreezing or plastic meniscus then ruptures or fails probably at or nearthe inner portion 218 and liquid metal again fills the area behind thefreezing meniscus restoring the submerged free liquid meniscus 220. Thefreezing metal surface which formed the freezing plastic meniscus 216generally is not completely redissolved by this inrushing action andremains as a permanent discontinuity extending from Ithe surface to aconsiderable depth into the solidified ingot.

In accordance with the invention the solution to the problem of severeand disproportionate lap penetration resides in Ithe provision of a gateopening only slightly smaller than the internal dimensions a-t the moldas indicated in FIG. l and shown in more detail in FIG. 3. Within thelimits set forth herein, such will alleviate the disproportionate lappenetration associated with the lower surface portions of horizontallycast ingot. Referring to FIG. 3 it is seen that the edge 312 of the gateopening 20 is only slightly inward of the inner mold wall surface. Inlaccordance with the invention this distance, the A dimension in FIG. 3,is highly critical and ranges broadly from 1,/64" to J/g" and ispreferably 1/16 to g". The A dimension is measured from the insidesurface 310 of any step at the mold entrance as indicated in FIGURE 3,since as the step seldom exceeds 0.020 into the mold opening, itssurface is considered the inner mold wall surface at the mold entrance.The slope at which the gate diverges into the mold can range from nil,or an attitude substantially parallel to the ingot axis, to a slope of60 with respect to the ingot axis although a range of 0 to 45 ispreferred. The edge 312 should be fairly sharp Iand is preferably notrounded more .than $64. Since the stream of molten metal will be movingquite slowly through such a large gate, the slope of the mold opening inthe header plate is only important at the discharge side of the plate.Hence the gate opening on the reservoir side of the plate may have adifferent slope than on the opposite side of the plate. For example,referring to FIG. 3, the mold side slope 316 only extends for a portionthrough the gate opening, the reservoir side portion 320 being straightor having a different slope.

In accordance with the method of the invention, molten metal isintroduced through the large gate opening at a slow linear rate which issubstantially the same as the ingot withdrawal rate. Typical withdrawalrates can range from one to ten inches per minute depending on the sizeof the ingot. The peripheral portion of the molten metal is introducedin close proximity to the mold wall, 1&4 to 1/s and preferably 1746" to3/32 from the mold inside wall at the mold entrance. Anotherconsideration is 'the attitude at which the surface portion of themolten metal reaches .the mold. This attitude is generally diverginginto the mold at an angle of 0 to 45 with respect to the mold axis. Thusthe attitude is described as having a substantial component parallel tothe mold axis. This method may be contrasted to the practice where thegate is relatively small in respect -to the cross-sectional dimension ofthe mold, and spaced `at a distance from the mold wall. There theperipheral or surface metal is introduced at a distance from the moldgreater than the maximum delined herein and moves outwardly over theheader plate where it contacts the mold at an attitude substantiallynormal to the ingot axis. Thus in accordance with the method of theinvention molten metal is introduced into the mold in a manner such thatthe peripheral or surface portions thereof enter Ithe mold at a slowlinear ow rate and in close proximity to its inner wall surface andfurther at an attitude having a substantial component parallel to themold axis. Another aspect is the action of the laps as they tend to growinto the ingot whereby they are deflected by the edge 312 of the gateopening toward an attitude parallel to the mold axis but in thedirection opposite the molten metal flowing through the gate opening.This deflection together with proper molten metal introduction as setforth above serves to minimize disproportionate lap penetration into theingot. At this point it should be understood that the theoreticaldiscussions and explanations as to the nature and cause of laps togetherwith the mechanism by which the invention achieves its objects aremerely intended to illustrate the invention with greater perspectiveland are not necessarily intended to place any limitation on theinvention. The benefits achieved by the invention are observablephenomena and need not be tied to `any theory.

To more clearly illustrate the practice of the invention the followingexample will proceed.

Example 1,-Several ingots of an aluminum alloy containing 3.5 to 5.0%magnesium, the balance being aluminum and impurities, were continuouslycast in horizontal molds. The ingots generally had rectangularcrosssections of about 16" x 39". In addition to magnesium some ingotscontained about 0.2 to 0.7% manganese and 0.05 to 0.25% chromium. Usingthe apparatus of the general type shown in FIGURE 1, but withoutincluding the limits required by the practice of the invention, severalingots were cast at an ingot withdrawal rate of about two inches perminute. These ingots all exhibited nonuni-form lap defect depth in thatthe depth across the midtop portion averaged around V16 but the depth atthe top corners, the sides and bottom, the zone designated 810 in FIG.4a is about Additional ingots were cast using the same basic castingapparatus with the gate opening modified in accordance with theinvention. Very good results were achieved where, referring to FIG. 3, Ais ym" to 1%2 and angle x is about 45, the ingots exhibiting a maximumlap penetration of about Ms to Still further improved results areobtained by holding the slope, angle x, within the range of to 25 whichis considered a preferred embodiment of the invention, not only for theparticular alloy composition specied in this example but for anyalmninum alloy.

It is to be understood that while reference to aluminum and toparticular alloys thereof appear in this description, such is not alimitation thereon. The invention will find application in thehorizontal continuous casting of any light metal which has a tendency toform disproportionately deep laps in the lower surface portions `ofhorizontal continuously cast ingot. By the light metals and their alloysis meant aluminum and magnesium or alloys thereof containing at least75% base metal. Also, while there have been shown and described what arepresently considered to be preferred embodiments of the inventiontogether with some minor variations, further modifications thereto willreadily occur to those skilled in the art. It is not desired, therefore,that the invention be limited to the specific arrangements described andthe appended claims are intended to include any modifications orvariations as fall within the true scope and spirit of the invention.

We claim:

1. An apparatus for the continuous casting of light metal ingotcomprising a molten metal reservoir, a Ihorizontally disposed mold incommunication with said reservoir, said mold having chilled walls and anentrance and exit, and having at its entrance a small inwardly extendingstep, a common non-chilling header plate between said reservoir and saidentrance of said mold except for a gate opening in said header plate forthe passage of molten metal from said reservoir to said mold, said gateopening being `only slightly smaller than the internal dimensions of themold entrance such that the distance from the edge of the gate openingoutwardly to the inner mold wall surface at the mold entrance rangesfrom %4 to Ms", the slope of the gate opening diverging into the mold atan angle of from 0 to 60 with respect to the mold axis, means forapplying lubricant to the inner mold wall surface at the entranceportion of said mold and substantially around the periphery thereof,means for cooling said mold and the ingot within and emerging therefromsubstantially around the periphery thereof, and means for withdrawingthe ingot from the mold at a relatively continuous rate.

2. 'Ihe apparatus as in claim 1 wherein the light metal contains atleast 75 aluminum.

3. An apparatus for the continuous casting of aluminum alloy ingotcomprising a molten metal reservoir, a horizontally disposed mold incommunication with said reservoir, said mold Ihaving chilled walls andan entrance and exit and having at its entrance a small inwardlyextending step, a common non-chilling header plate between saidreservoir and said entrance of said mold except for a gate opening insaid header plate for the passage of molten metal from said reservoir tosaid mold, said gate opening being only slightly smaller than theinternal dimensions of the mold entrance such that the distance from theedge of the gate opening outwardly to the inner mold wall surface at themold entrance ranges from 1/16 to %2, the slope of the gate openingdiverging into the mold at an angle of from 0 to 45 with respect to themold axis, means for applying lubricant to the inner mold wall surfaceat the entrance portion of said mold and substantially around theperiphery thereof, means for cooling said mold and the ingot within andemerging therefrom substantially around the periphery thereof, and meansfor withdrawing the ingot from the mold at a relatively continuous rate.

y4. The apparatus as in claim 3 wherein the slope of the gate openingdiverges into the 4mold at an angle of from 15 to 25 with respect to themold axis.

References Cited UNITED STATES PATENTS 2,565,959 8/1951 Francis et al.2257.2 X 2,996,771 8/ 1961 Armand et al. 22-572 3,022,552 2/ 1962Tessmann 22-57.2 3,045,299 7/1962 Steigerwald 22-57.2 3,076,241 2/ 1963Simonson et al. 22-57.2 X 3,263,283 8/ 1966 Allard 2257.2

J. SPENCER OVERHOLSER, Primary Examiner. R. S. ANNEAR, AssistantExaminer.

1. AN APPARATUS FOR THE CONTINUOUS CASTING OF LIGHT METAL INGOTCOMPRISING A MOLTEN METAL RESERVOIR, A HORIZONTALLY DISPOSED MOLD INCOMMUNICATION WITH SAID RESERVOIR, SAID MOLD HAVING CHILLED WALLS AND ANENTRANCE AND EXIT, AND HAVING AT ITS ENTRANCE A SMALL INWARDLY EXTENDINGSTEP, A COMMON NON-CHILLING HEADER PLATE BETWEEN SAID RESERVOIR AND SAIDENTRANCE OF SAID MOLD EXCEPT FOR A GATE OPENING IN SAID HEADER PLATE FORTHE PASSAGE OF MOLTEN METAL FROM SAID RESERVOIR TO SAID MOLD, SAID GATEOPENING BEING ONLY SLIGHTLY SMALLER THAN THE INTERNAL DIMENSIONS OF THEMOLD ENTRANCE SUCH THAT THE DISTANCE FROM THE EDGE OF THE GATE OPENINGOUTWARDLY TO THE INNER MOLD WALL SURFACE AT THE MOLD ENTRANCE RANGESFROM 1/64" TO 1/8", THE SLOPE OF THE GATE OPENING DIVERGING INTO THEMOLD AT AN ANGLE OF FROM 0* TO 60* WITH RESPECT TO THE MOLD AXIS, MEANSFOR APPLYING LUBRICANT TO THE INNER MOLD WALL SURFACE AT THE ENTRANCEPORTION OF SAID MOLD AND SUBSTANTIALLY AROUND THE PERIPHERY THEREOF,MEANS FOR COOLING SAID MOLD AND THE INGOT WITHIN AND EMERGING THEREFROMSUBSTANTIALLY AROUND THE PERIPHERY THEREOF, AND MEANS FOR WITHDRAWINGTHE INGOT FROM THE MOLD AT A RELATIVELY CONTINUOUS RATE.